This invention relates generally to an adhesive treatment for fibers or a tensile cord for reinforcement of polymeric or elastomeric products such as power transmission belts and hose, more particularly to an aqueous adhesive treatment for fibers such as carbon fiber, which include a primer material such as an epoxy, a polyelectrolyte material such as a maleated polybutadiene derivative, and a curative such as an organic peroxide or a sulfur-based curative.
The most common fiber bonding system in the reinforced rubber product arts is based on primed fiber treated with resorcinol-formaldehyde-latex (“RFL”) adhesive. U.S. Pat. No. 6,857,159 B2, the contents of which are hereby incorporated herein by reference, is an example disclosing the use of RFL on carbon fiber tensile cords for rubber belts. Many variations for the RFL adhesive have been proposed.
Various supplemental adhesion promoters have been proposed to enhance the usefulness of the RFL. One example is EP 1,451,244 B1 which discloses a primer consisting of a ring-opened, maleinized polybutadiene and a phenolic derivative. Also proposed is that the primer may be used as an additive to the RFL to reduce the number of dipping stages. Other adhesion promoters have been added to RFL.
Another example of a variation of the RFL is removal of the RF resin component and substitution of an alternate material to promote adhesion or provide other properties. U.S. Pat. No. 7,256,235 B2 discloses an adhesive composition comprising a latex of a hydrogenated styrene-butadiene rubber, a carboxylated hydrogenated styrene-butadiene rubber, a hydrogenated nitrile-butadiene rubber, a carboxylated hydrogenated nitrile-butadiene rubber, a chlorosulfonated polyethylene or blends thereof; plus an aqueous solution of a half-ester of maleinized liquid poly butadiene; and, optionally, up to about 15% by weight carbon black in an aqueous solution. Examples on isocyanate-pretreated polyester cord are disclosed.
U.S. Pat. No. 7,067,189 B2 discloses an adhesion promoter comprising a polymeric strand with an epoxy-reactive group other than a phenolic hydroxyl group, and a crosslinking group that crosslinks the polymeric strand with a rubber in a crosslinking reaction. The adhesion promoter combined with a styrene-butadiene-vinylpyridine latex increases adhesion of rubber to polymeric fibers. The adhesion promoter may also be added to the rubber. Examples disclosed are based on epoxy-finished polyester cords in SBR and BR rubber compounds.
In the power transmission belt art, while achieving excellent cord-to-rubber adhesion is needed for enhanced belt life, it is equally important for the cord to exhibit good flex-fatigue to maintain performance particularly in belt applications where severe belt bending occurs throughout the service life. Realizing the right balance of excellent cord adhesion and belt flex-fatigue has been a fundamental challenge in many belt designs, in part because most of the conventional adhesive systems (such as RFL) become relatively rigid within the cord bundle and at the cord-rubber body interface after vulcanization. As a result, when such belt is subjected to repeat flexing or back bends the adhesive layer becomes more brittle and delaminates leading to belt failures. Failure modes may include cord tensile failure, adhesive delamination, edge-cord pull, etc. Therefore, an adhesive system that can provide both excellent cord adhesion and flex-fatigue would be desirable, especially for use with high-modulus, high-stiffness, tensile members such as carbon-fiber cords.